This invention relates to seals for turbine applications and particularly to seals between combustor transition pieces and stage one turbine nozzles.
Sealing is oftentimes essential in rotary machines, especially when there are two relatively movable mechanical members in close proximity to one another. For example, sealing is required to prevent or at least minimize leakage of combustion gases at the interface between combustor transition pieces and stage one nozzles of gas turbines.
In can-annular combustor arrangements typically found in gas turbines manufactured by the assignee, a plurality of combustors are disposed in an annular array about the axis of the turbine. Hot combustion gases flow from each combustor through a respective transition piece into the first stage nozzle. In addition to relative movement (due, e.g., to dynamic pulsing) between these components, the transition pieces and first stage nozzle are formed of different materials and are thus subjected to different temperatures during operation, thereby experiencing different degrees of thermal growth. Thus, both the transition pieces and the first stage nozzle and/or nozzle support elements may move radially, circumferentially and axially relative to one another. This xe2x80x9cmismatchxe2x80x9d at the interface of the transition pieces and the first stage nozzle and/or nozzle support elements requires an effective seal to contain the combustion products and the pressure differential across that interface, and to prevent compressor discharge air from bypassing the combustor.
It is known to employ a dual stiffness cloth brush seal for sealing between combustor transition pieces and first stage nozzles or nozzle supports. Specifically, the layers of cloth material are disposed in a frame and suitably secured thereto, for example, by clamping to the frame, welding the material to the frame, or the like. The free edge of the layers are engaged within a U-shaped channel extending about the periphery of the downstream end of each transition piece, while a seal support is mounted within a groove or slot formed in the first stage nozzle or nozzle support. A cloth brush seal of this type is disclosed in commonly owned U.S. Pat. No. 6,042,119. This seal is not completely effective, however. For example, the inner and outer side walls of the stage one nozzle are unevenly heated, due to varied velocities on the pressure and suction sides of the nozzle. This causes the groove or slot where the seal support is secured to unevenly distort. This distortion, in effect, lifts the transition piece seal off its pressure sealing surface in the groove or slot, causing compressor discharge air to bypass the combustor, thereby increasing the levels of NOx emitted to atmosphere.
This invention seeks to minimize leakage by combining the transition piece seal with flexible spring seal elements that provide better leakage control at the interface of the transition piece and the stage one nozzle or nozzle support. For purposes of this disclosure, it matters not whether the spring seal element engages the nozzle itself or a nozzle support element. Thus, reference will be made herein simply to the first stage nozzle.
Specifically, each flexible spring seal element includes a generally horizontal mounting flange that enables the spring seal element to be secured within the slot formed in the first stage nozzle, along with the transition piece seal support. The remainder of the spring seal element has a sideways S or Z shape, with a flexible free end of the seal element adapted to engage the forward face of the first stage nozzle. The spring seal element is formed with a plurality of laterally spaced, axially oriented slots extending from the free sealing edge substantially to the horizontal mounting flange so that the spring seal element can differentially adapt or conform to the forward face of the first stage nozzle. To prevent leakage through the slots, a second substantially identical spring seal element is layered over the first spring seal element, but laterally offset in a shingled arrangement, thereby closing the slots in the respective spring elements. When the spring seal elements are mounted in the groove or slot in the first stage nozzle, along with the transition piece seal support, the free ends of the spring seal elements are resiliently compressed or biased against the forward face of the stage one nozzle, creating a first sealing location. At the same time, axial compression of the sealing elements also results in a downward force on the mounting flange, pushing the transition piece seal support against the lower surface of the groove or slot in the first stage nozzle, creating a second seal location.
Accordingly, in its broader aspects, the present invention relates to a transition piece seal assembly comprising a transition piece seal support having a first flange for supporting a transition piece seal, and a second flange adapted for mounting in an adjacent nozzle; and at least one spring seal element having a mounting flange adapted to engage the second flange of the transition piece seal support, and a flex portion having a free edge adapted to engage a forward face of the nozzle.
In another aspect, the invention relates to a gas turbine comprising an annular array of combustors, each having a transition piece extending between the combustor and a first stage turbine nozzle, and wherein a transition piece seal assembly is interposed at the interface of each transition piece and the first stage turbine nozzle, each transition piece seal assembly comprising a transition piece seal support having a first flange for supporting a transition piece seal, and a second flange secured in the first stage turbine nozzle; and at least one spring seal element having a mounting flange seated on the second flange of the transition piece seal support, and a flex portion having a free edge compressively engaged with a forward face of the nozzle.
In still another aspect, the invention relates to a method of reducing leakage at an interface of a transition piece and a first stage turbine nozzle comprising: a) providing a seal assembly between the transition piece and the first stage turbine nozzle wherein the transition piece seal assembly is supported on a forward face of the first stage turbine nozzle and includes a seal support supporting sealing media engaged in a peripheral slot or channel on the transition piece; and b) providing at least one additional sealing element supported at one end in the forward face of the first stage turbine nozzle and having a free edge remote from the one end engaged with the forward face of the first stage turbine nozzle.